Assessment of murine colorectal cancer by micro-ultrasound using three-dimensional reconstruction and non-linear contrast imaging

The relatively low success rates of current colorectal cancer therapies have led investigators to search for more specific treatments. Vertebrate models of colorectal cancer are essential tools for the verification of new therapeutic avenues such as gene therapy. The evaluation of colorectal cancer in mouse models has been limited due to the lack of an accurate quantitative and longitudinal non-invasive method. The current work introduces a method of three-dimensional micro-ultrasound reconstruction and microbubble administration for the comprehensive and longitudinal evaluation of colorectal cancer progression. This approach enabled quantification of both tumor volume and relative vascularity using a well-established inducible murine model of colon carcinogenesis. This inducible model recapitulated the adeno-carcinoma sequence that occurs in human colorectal cancer allowing systematic in situ evaluation of the ultrasound technique. The administration of intravenous microbubbles facilitated enhancement of colon vascular contrast and quantification of relative vascularity of the mid and distal colon of the mouse in three dimensions. In addition, twodimensional imaging in the sagittal orientation of the colon using Non- Linear Contrast Mode enabled calculation of relative blood volume and perfusion as the micro bubbles entered the colon micro-vasculature. Quantitative results provided by the outlined protocol represent a noninvasive tool that can more accurately define colorectal cancer development and progression. This ultrasound technique will allow the practical and economical longitudinal study of murine colorectal cancer in both basic and pre-clinical studies.